JP4608272B2 - Insulation resistance measuring method and apparatus, and latent image carrier evaluation method - Google Patents

Description

The present invention relates to an insulation resistance measuring method and apparatus and a latent image carrier evaluation method .

Dielectric materials and dielectric materials are widely used in every field of industry, and their characteristic insulation resistance is extremely important.
Since the dielectric is in an electrically insulated state, electrons and holes do not flow through the dielectric, but local dielectric breakdown occurs at portions where the electric field strength in the dielectric is strong and exceeds the withstand voltage. As for the state of dielectric breakdown, it is possible to observe the state where the surface and the inside of the dielectric are mechanically broken with an optical microscope or the like with high resolution. The cause cannot be analyzed. It is desired to measure a local dielectric breakdown state in a state where it is not yet broken mechanically but is electrically broken. If it is possible to identify the “where” the dielectric breakdown occurs under what conditions, the cause can be analyzed.

  An example of a matter in which dielectric quality is an important issue is a well-known “photoconductive photoreceptor” related to an image forming apparatus such as an electronic copying machine or an optical printer. The photoconductive photoconductor is dielectric in the dark, and after being uniformly charged, an image is written by exposure to form an electrostatic latent image. In such a photoreceptor, it is necessary that the insulation resistance, which is the quality of the dielectric in the region where the electrostatic latent image is to be formed, be uniform.

  As an example, when looking at a function-separated type photoreceptor, as is well known, the function-separated type photoreceptor has an undercoat layer formed on a conductive substrate, and charges are generated on the undercoat layer. The layer and the charge transport layer are stacked. The undercoat layer is provided for the purpose of preventing leakage of charged charges due to charge injection from the substrate side. However, in general, since a charge leak is likely to occur in a high electric field, an undercoat layer that can withstand this is desired.

  When an electrostatic ray image is formed on such a function-separated type photoconductor, the surface of the photoconductor is uniformly charged at a high potential, and the charge that uniformly charges the surface of the photoconductor and the boundary between the substrate and the undercoat layer are generated by this charge. High electric fields are applied to the undercoat layer, the charge generation layer, and the charge transport layer due to the “inverse polarity charge induced in the part”.

  At this time, if there are defective parts or “electrically abnormal parts” in the undercoat layer, these parts cannot withstand a high electric field and allow holes to flow from the substrate. When passing through the charge transport layer and reaching the surface of the photoreceptor, the charged charge is neutralized. Therefore, in such a portion, the surface potential of the photoconductor is lowered to be “as if exposed”.

  Such a potential drop does not appear as an abnormality in the formed image in the initial stage, but as the number of images formed increases, electrostatic fatigue accumulates at the above-mentioned site, and the potential drop gradually increases. As a result, when the photoreceptor surface potential becomes smaller than the developing bias, the toner to be reversely developed adheres to such a portion, resulting in an image abnormality.

  Defects and electrically abnormal parts in the undercoat layer are randomly scattered in pinpoint form, and the above-mentioned image abnormality occurs in a state where dot-like stains are randomly scattered in accordance with these. .

As described above, the electrical defect portion included in the photoconductor can be grasped to some extent by visualizing the photoconductor as a toner image after uniformly charging the photoconductor. -It is not always easy to identify whether it is due to abnormalities such as transfer or fixing.
Therefore, a method for evaluating the insulation resistance of a photoreceptor or the like on the order of μm is desired.

  Patent documents 1 and 2 relating to the measurement of electrostatic latent images proposed by the inventor and used in principle in the present invention are listed as patent documents.

JP 2003-295696 A JP2003-305882A

It is an object of the present invention to realize an insulation resistance measuring method and apparatus capable of evaluating the insulation resistance of a latent image carrier such as a photoreceptor with a precision on the order of μm, and to realize a good photoreceptor in terms of insulation resistance. To do.

The insulation resistance measuring method of the present invention has the following characteristics (claim 1).
That is, the surface of the sample that has been charged and given an electric field strength in the thickness direction is scanned two-dimensionally with an electron beam, and “insulation resistance of the sample” is evaluated based on the detection signal obtained by this scanning.
The sample to be measured is a latent image carrier and is dielectric, and charging the sample generally means adding a charged charge to the surface of the sample. The charge when the sample is charged does not necessarily exist only on the sample surface, but may exist in a “surface layer region” that is not so deep from the sample surface. Therefore, in this specification, the state in which the surface of the sample is charged is “the distribution of the charged charge is three-dimensional, but the distribution in the sample surface direction compared to the distribution region in the depth direction from the sample surface. Is included in a sufficiently large state. The “latent image carrier” will be described later.
The latent image carrier, which is a sample, is charged by two-dimensionally scanning a “charged electron beam” with respect to a desired region of the sample surface, and a predetermined electric field intensity is measured in the thickness direction of the sample in the desired region. give.
The “charge potential of the sample” corresponding to the applied electric field strength is two-dimensionally scanned by the “electron beam for potential detection”, and the desired region is charged by detecting the secondary electrons accompanying this scanning. The state is acquired as “two-dimensional image data”, and the insulation resistance of the sample is evaluated based on this image data.
The acceleration voltage of the electron beam that performs two-dimensional scanning with the charging electron beam is higher than the acceleration voltage E2 that becomes 2 after the secondary electron emission ratio δ from the sample surface exceeds the maximum at the time of scanning. High acceleration voltage: set to E (> E2). By setting the acceleration voltage of the charging electron beam in this way, the desired region on the surface of the latent image carrier is charged to a negative polarity.
In the above, for example, “secondary electron emission ratio: δ” means that the secondary electron emission ratio is represented by the symbol “δ”. The same applies to other quantities such as acceleration voltage. The definition of “secondary electron emission ratio” will be described later.
“Two-dimensional scanning with an electron beam for potential detection” is performed with an irradiation current amount different from that when scanning with an electron beam for charging.
The insulation resistance measuring method is preferably “gives an electric field strength of 10 V / μm or more in the thickness direction of the sample” by two-dimensional scanning with an electron beam for charging.
This is because if the electric field strength applied in the thickness direction of the sample is smaller than the above, dielectric breakdown is unlikely to occur and evaluation may be difficult. Of course, it goes without saying that the electric field strength is not charged so as to cause dielectric breakdown over the entire charged region of the latent image carrier.

An insulation resistance measuring apparatus according to the present invention is an apparatus that performs the above measuring method, and includes a holding unit, a charging unit, a scanning unit, a signal detecting unit, and an evaluating unit .
“Holding means” is means for holding a sample (latent image carrier) whose insulation resistance is to be evaluated.
“Holding a sample” means holding a sample whose insulation resistance is to be evaluated in a measurable state.

"Charging means" charges the sample held by the holding means, Ri means der applying an electric field strength in the thickness direction of the sample, two-dimensional desired two-dimensional area of the sample by the electron beam for charge To scan .
The “scanning unit” is a unit that scans the surface of the charged sample with an electron beam. However , the “scanning unit” scans the desired two-dimensional region two-dimensionally with a detection electron beam whose irradiation current is switched in the charging unit. .
A “charged particle beam” is an electron beam (also referred to as an electron beam ) , and a sample is scanned two-dimensionally by an electron beam.

“Signal detection means” is means for obtaining a detection signal by scanning by the scanning means.
The “evaluation means” is a means for evaluating the insulation resistance of the sample based on the signal detected by the signal detection means, and is configured using a computer, a microprocessor or the like, and performs necessary processing such as calculation based on the detection signal. .

The evaluation means acquires the charged state of the desired region as two-dimensional image data, and the insulation resistance is evaluated based on the image data.

As described above, the “electron beam that scans the surface of the sample two-dimensionally ” is used for charging the latent image carrier and detecting the charged potential according to the charged state. Scans the desired two-dimensional region two-dimensionally by “a detection electron beam whose irradiation current in the charging means is switched”.
In the two-dimensional scanning with the charging electron beam, the acceleration voltage of the electron beam becomes 1 after the secondary electron emission ratio δ from the sample surface accompanying the scanning exceeds the maximum value: E2 Higher acceleration voltage: E (> E2) .

The scanning means (charging means) that scans the electron beam has a condenser lens and an aperture, and the condenser lens and / or the aperture causes the irradiation current amount to “charge the sample” and “detection signal”. You can switch between when you get . Since such switching can be “instantaneous switching”, it is possible to perform “measurement in a transient state” with this configuration.

In the insulation resistance measuring device, “secondary electrons generated from the sample by scanning with an electron beam” are detected to obtain a detection signal. The “secondary electrons” referred to here are not only secondary electrons emitted from the sample by irradiation of the electron beam, but also irradiation of electron beams such as so-called tertiary electrons emitted when the secondary electrons collide with the sample. In general, electrons emitted from the sample due to the above are included. The same applies to scanning with a charged particle beam other than an electron beam, such as an ion beam.

“ Based on a detection signal obtained by detecting secondary electrons , it is possible to detect a charge leak point in the sample .
The “latent image carrier” is a medium that carries an electrostatic latent image, and can be various photoconductive photoreceptors and dielectric media that have been widely known.

The latent image carrier evaluation method according to claim 4 is a method for evaluating suitability as a latent image carrier using the latent image carrier as a sample, and the electric field strength applied in the thickness direction is 30 V / μm or more. When the sample (latent image carrier) is irradiated with an electron beam for charging at 1E-8 coulomb / mm ² or more under the condition of 40 V / μm or less, the “ resistance resistance according to any one of claims 1 to 3”. Whether or not the area of the insulating region measured by the insulation measurement method (the area of the evaluation region that evaluates the insulation resistance of the sample that does not break down) is 99% or more of the evaluation region area of the sample. Accordingly, the suitability of the latent image carrier is determined.
1E-8 coulomb / mm ² means “1 × 10 ⁻⁸ coulomb / mm ² ”. The same applies to the following.

The latent image bearing member evaluation method according to claim 4, wherein the electric field intensity in the thickness direction of the sample is 30 V / μm or more and 40 V / μm or less, and the charging electron beam is 1E-8 coulomb / mm ² or more. When irradiated, the area of the charge leakage region is 0.05% or more and 1.0% or less of the evaluation region area , so that it can be evaluated as a good latent image carrier.

The charge irradiation is performed by a charging electron beam.

According to the insulation resistance measuring method and apparatus of the present invention, the insulation resistance of the dielectric sample or the latent image carrier, which is a dielectric sample , is not mechanically destroyed, but the sample is not electrically destroyed. It is possible to measure the local dielectric breakdown state in the existing state and the insulation resistance state of the manufactured latent image carrier with an accuracy of the order of μm. By this measurement, the cause of the dielectric breakdown in the sample can be analyzed.

Also, the latent image carrier evaluation method of the present invention can evaluate whether or not the insulation resistance is above a certain level by measuring and evaluating the insulation resistance with an accuracy of μm order with the measurement method / measurement apparatus.

Embodiments of the invention will be described below.
The insulation resistance measuring apparatus shown in FIG. 1 is an apparatus for evaluating the insulation resistance of a thin plate-like dielectric sample 0.
In FIG. 1A, a dielectric sample 0 to be evaluated for insulation resistance is placed in close contact with a grounded conductive plate-like holding portion 23. An electron beam irradiation unit 11A is arranged above the surface side of the placed dielectric sample 0.

  The electron beam irradiation unit 11A includes an electron gun 10 that emits an electron beam, a beam monitor 13, a condenser lens 15, an aperture 17, a beam blanker 18, a scanning lens 19, and an objective lens 21. These are connected to a power source (not shown) and controlled by a control means (not shown) such as a computer.

  The beam monitor 13 is for monitoring the intensity of the electron beam emitted from the electron gun 10, and the condenser lens 15 is an electron lens for focusing the electron beam emitted from the electron gun 10. The aperture 17 is for controlling the current density (number of irradiation potentials per unit time) of the irradiation current by the electron beam, and the beam blanker 18 turns the electron beam irradiated on the dielectric sample 0 ON / OFF. It is for making it happen.

  The scanning lens 19 is a “deflection coil” for two-dimensionally scanning the electron beam that has passed through the beam blanker 18, and the objective lens 21 focuses the scanned electron beam toward the surface of the dielectric sample 0. It is for making it happen.

  That is, the electron beam radiated from the electron gun 10 passes through the beam monitor 13, passes through the position of the aperture 17 and the beam blanker 18 by the condenser lens 15, and passes two-dimensionally by the scanning lens 19 over the deflection coil. Biased. The electron beam deflected in this way is focused toward the surface of the dielectric sample 0 by the objective lens 21.

As described above, the electron beam deflected two-dimensionally by the scanning lens 19 scans the surface of the dielectric sample 0 two-dimensionally.
That is, the electron beam irradiation unit 11A and the control means constitute a “scanning means”.

  In FIG. 1A, reference numeral 25 denotes a “charged particle trap”. A signal output from the charged particle trap 25 is sent to a signal processing unit (not shown) (for example, it can be configured as a part of the function of a computer forming the above-described control means), and the signal processing unit is input. According to the information, a predetermined process is performed to evaluate the insulation resistance of the dielectric sample 0.

That is, the charged particle trap 25 constitutes “signal detection means”. Further, a signal processing unit (not shown) constitutes “evaluation means”.
The electron beam irradiation unit 11A, the plate-like holding unit 23, and the charged particle trap 25 are housed in a sealed casing 30A, and the inside of the sealed casing 30A can be decompressed to a “substantially vacuum state” by the suction means 32. Yes. The suction means 32 is controlled by the control means (not shown). Therefore, the plate-like holding portion 23, the sealed casing 30A, the suction means 32, and the control means (not shown) constitute “a holding means for holding a sample whose insulation resistance is to be evaluated”.
In this embodiment, the aforementioned “scanning means” is also used as the “charging means”.

  Hereinafter, an example of evaluating the insulation resistance when the dielectric sample 0 is a thin plate polycarbonate (PC) using the apparatus of FIG. 1A will be described. Since the insulation resistance of PC is “about 20 V / μm”, if this is the evaluation value this time, if the thickness of the dielectric sample is 50 μm, a charging potential of 1 kV or more in the thickness direction is applied. Give it.

  First, the dielectric sample 0 is charged by scanning with an electron beam. That is, the dielectric sample 0 is charged using the scanning unit as the charging unit. Charging is performed so that the surface side of the dielectric sample 0 has a negative polarity.

  When “using the scanning unit as the charging unit”, shortening the charging time by setting the irradiation current during charging “larger than the irradiation current during signal detection” leads to a reduction in measurement time. In order to electrically switch the irradiation current amount (current density), it is preferable to electrically change the focal length of the condenser lens 15 and change the amount of current passing through the aperture 17.

  That is, as shown in FIG. 1B, the irradiation current is large if the electron beam is focused on the opening of the aperture 17 by the condenser lens 15, but as shown in FIG. When the focal length is shortened, the electron beam is focused in front of the aperture 17 and divergently enters the aperture 17, so that a part of the electron beam is blocked by the aperture 17, and the dielectric sample 0. The irradiation current going to becomes smaller. Even if the focal length of the condenser lens 15 is longer than that in the case of FIG. 1B, the irradiation current can be reduced in the same manner as described above.

  It is also possible to change the magnitude of the irradiation current by changing the aperture diameter of the aperture 17. In addition, the irradiation current can be switched or changed by adjusting the aperture 17 and the condenser lens 15. In the example being described, the condenser lens 15 is a “magnetic lens”, but the same applies to an electric field lens.

  When charging the dielectric sample 0, the irradiation current is made larger than that at the time of signal detection as described above, and the measurement region (for example, 1 mm square) on the surface of the dielectric sample 0 is scanned two-dimensionally. At this time, the charge polarity of the dielectric sample 0 differs depending on the magnitude of the acceleration voltage E of the electron beam.

  That is, the secondary electron emission ratio: δ is defined as Not / Nin, where Not is the number of secondary electrons emitted with respect to the number of incident electrons irradiated: Nin. When the acceleration voltage is gradually increased from 0 to increase the energy of the electron beam, the number of secondary electrons emitted initially increases, but the number of secondary electrons takes a maximum as the acceleration voltage increases and then decreases. .

  That is, as the acceleration voltage increases, the secondary electron emission ratio: δ first increases, and when the acceleration voltage: E1, δ = 1. After that, when the acceleration voltage increases, the maximum value is reached, and then the acceleration voltage: E2 or more and 1 or less. To decrease. Therefore, when the acceleration voltage E is set to “range of E1 ≦ E ≦ E2”, the surface of the dielectric sample 0 is charged positively as the electron beam is scanned.

In the example in the description, the acceleration voltage (E> E2) higher than the acceleration voltage E2 (E> E2) that becomes 1 after the secondary electron emission ratio δ exceeds the maximum is set to be negatively charged. When two-dimensional scanning is performed in this way, the amount of incident electrons by scanning exceeds the amount of emitted electrons, so that electrons are accumulated on the surface layer of the dielectric sample 0, and the surface side of the dielectric sample 0 is uniformly negative. Charge. In FIG. 1A, the symbol C indicates “accumulated electrons”. FIG. 1A shows a state in which the surface of the dielectric sample 0 is positively charged.

In addition, since the plate-like holding portion 23 that is in close contact with the back surface side of the dielectric sample 0 is electrically conductive and grounded, the positive charge that balances the “negative charge on the front surface side” of the dielectric sample 0 (in FIG. 1A). (Indicated by symbol D) is induced at the boundary surface with the dielectric sample 0, and the electric field strength is given in the thickness direction of the dielectric sample 0. Acceleration voltage: A desired charging potential can be formed by appropriately setting E and irradiation time .

  If the dielectric sample 0 continues to be charged after reaching the charging potential of 1 kV, the charging voltage increases, and a dielectric breakdown occurs in a part having a poor insulation resistance, and a hole is formed in the dielectric sample 0 from the plate-shaped holding portion 23. Flows in and cancels out the negative charge on the sample surface side. Such electrical cancellation locally occurs and a charge distribution is generated on the surface side of the dielectric sample 0. An electric field distribution corresponding to the surface charge distribution is formed in the space on the surface side of the dielectric sample 0.

  In this state, the current amount of the irradiation current by the scanning means is switched to “for signal detection” to perform two-dimensional scanning for signal detection. Then, secondary electrons es are captured by the charged particle trap 25. The charged particle trap 25 is a combination of a scintillator (phosphor) and a photomultiplier tube, and the secondary electrons es are captured by the scintillator by an electric field of “attraction voltage applied to the surface of the scintillator by a power source (not shown)”. And converted into scintillation light. This light passes through the light pipe, is amplified as a current by a photomultiplier tube, and is extracted as a detection signal (current signal).

  FIG. 2A illustrates the potential distribution in the space between the scintillator 24 and the dielectric sample 0 in the charged particle trap 25 by “contour line display”. The surface of the dielectric sample 0 is in a state of being uniformly charged negatively except for “the portion where the potential is attenuated by dielectric breakdown”, and a positive potential is applied to the scintillator 24 of the charged particle trap 25. Therefore, in the “potential contour line group indicated by a solid line”, the “potential increases” as it approaches the scintillator 24 from the surface of the dielectric sample 0.

  Therefore, the secondary electrons el1 and el2 generated at the points Q1 and Q2 in the figure, which are “negatively uniformly charged portions” in the dielectric sample 0, are attracted to the positive potential of the charged particle trap 24, It is displaced as shown by arrows G1 and G2 and is captured by the scintillator 24.

On the other hand, in FIG. 2A , the point Q3 is “a portion where the negative potential is attenuated due to dielectric breakdown”, and the arrangement of potential contour lines is “as shown by the broken line” in the vicinity of the point Q3. The closer to Q3 point, the higher the potential ”. In other words, an electric force constrained to the dielectric sample 0 side acts on the secondary electron el3 generated in the vicinity of the point Q3, as indicated by an arrow G3.

For this reason, the secondary electron el3 is captured in the “potential hole” indicated by the broken line potential contour and does not move toward the charged particle trap 24. FIG. 2B schematically shows the “potential hole”.

That is, the intensity of secondary electrons (number of secondary electrons) detected by the charged particle trap 25 is such that the high intensity portion is “a normal portion that is not dielectrically broken (a portion that is uniformly negatively charged) corresponds to the portion) "represented by point Q1 or Q2 in FIG. 2 (a), a point Q3 portions small portion of strength to the negative potential by" breakdown decreased as the absolute value (FIGS. 2 (a) This will correspond to “represented part)”.

At this time, “a region scanned two-dimensionally by an electron beam (evaluation region): S” is represented by S (x, y) in two-dimensional coordinates. For example, 0 mm ≦ x ≦ 1 mm and 0 mm ≦ y ≦ 1 mm. The surface potential distribution formed in this region: S (x, y) is V (x, y) (<0).
Assuming that the time from the start to the end of the two-dimensional scanning of the dielectric sample 0 by the electron beam is T ₀ ≦ T ≦ _TF , the time when scanning is performed: T is the scanning region: S ( It corresponds to each scanning position in x, y) 1: 1.

Therefore, by sampling the electrical signal (detection signal) obtained by the secondary electron detector 25 at an appropriate sampling time by the signal processor, the surface potential distribution: V (X, Y) using the sampling time: τ as a parameter. ) Can be specified for each “small area corresponding to sampling”, and the signal processing unit configures the surface potential distribution: V (X, Y) as two-dimensional image data, which is output device (not shown). Output as part of the evaluation means), the state of dielectric breakdown in the evaluation region can be obtained as a visible image.

  For example, if the intensity of captured secondary electrons is expressed as “brightness or weakness”, the image portion of the normal portion that is uniformly negatively charged is bright and the portion where dielectric breakdown has occurred (potential decayed portion) Can be output as a dark and contrasted bright and dark image. Even if the actual evaluation area is very small, the image output from the output device can be appropriately enlarged to “a desired size suitable for observation”.

  In this manner, it is possible to specify whether the dielectric sample 0 has undergone dielectric breakdown or where the dielectric breakdown has occurred, and as a result, the insulation resistance can be evaluated.

That is, the insulation resistance measuring apparatus described with reference to FIG. 1 charges the holding means 23, 30A, 32 and the like holding the sample 0 whose insulation resistance is to be evaluated, and the sample 0 held by the holding means, Charging means 11A for applying electric field strength in the thickness direction of the sample, scanning means 11A for scanning the surface of the charged sample 0 with a charged particle beam, and signal detection means 25 for obtaining a detection signal by scanning with the scanning means , and a evaluation means for evaluating the dielectric strength of the sample 0, based on the signal detected by the signal detection unit (signal processing unit (not shown)).

Further, an electric field strength of 10 V / μm or more is given in the thickness direction of the sample 0, an electron beam is used as a charged particle beam that scans the surface of the sample 0, and the scanning means 11A that scans the electron beam charges the sample 0 Used as a charging means.

Further, the scanning means for scanning the electron beam has the condenser lens 15 and the aperture 17, and the irradiation current amount is detected by the condenser lens 15 and / or the aperture 17 when the sample 0 is charged and the detection signal. It switches in and when you get. Then, secondary electrons generated from the sample 0 are detected by scanning with an electron beam to obtain a detection signal.

In the above embodiment, based on the detection signal obtained by detecting secondary electrons "Detection of charge leakage portion in the sample (portion to potential decay by charge leakage caused by insulation breakdown)" it is performed.

According to the insulation resistance measuring apparatus shown in FIG. 1, the surface of the sample 0 that has been charged and given an electric field strength in the thickness direction is two-dimensionally scanned with a charged particle beam, and a detection signal obtained by the scanning is obtained. Based on the above, an insulation resistance measuring method for evaluating the insulation resistance of the sample 0 is implemented .

Resistance to dielectric edge measurement device shown in FIG. 1 can also perform measurements of the latent image bearing member as a "sample to be evaluated insulation resistance". Hereinafter, such a case will be described.
As the latent image carrier, the above-described “function-separated type photoconductor” is taken as an example. FIG. 3A schematically illustrates the structure of the function-separated type photoconductor 01 in an explanatory manner. As is well known, the photoreceptor 01 has a configuration in which an undercoat layer 110 is formed on a conductive substrate 100, and a charge generation layer 120 and a charge transport layer 130 are stacked on the undercoat layer 110. ing.

  In FIG. 3A, such a photosensitive member (latent image carrier) is placed on the plate-like holding unit 23 of FIG. 1 as a dielectric sample 01, and as in the previous embodiment, A state in which the surface layer is negatively charged with electrons C by scanning with an electron beam is shown. At this time, positive charges D are injected from the plate-like holding portion 23 into the conductive substrate 100 and are induced at the boundary with the undercoat layer 110.

The upper diagram of FIG. 3B schematically shows a state in which dielectric breakdown has occurred in the portions indicated by reference numerals DM1 and DM2 of the photoreceptor 01. In these portions DM1 and DM2, holes (holes) are injected into the undercoat layer 110 from the substrate 100 side, and move through the charge generation layer 120 and the charge transport layer 130 to cancel the negative charges on the surface of the photoreceptor. Due to this cancellation, the charging potential is attenuated in these portions. The lower diagram of FIG. 3B schematically shows this potential decay state.
As described above, this state is scanned with an electron beam, secondary electrons generated along with the scanning are captured by a charged particle trap 25 to obtain a detection signal, which is processed by a signal processing unit. For example, if a dielectric breakdown state (charge leakage portion) is visualized, a visual image as shown in FIG. 3C is obtained.

As a specific example, when the film thickness of the photoconductor 100 (total thickness of the undercoat layer 110, the charge generation layer 120, and the charge transport layer 130): d = 30 μm and the charging potential: V = −900V, The absolute value of the electric field strength applied in the thickness direction: EA is
EA = | V / d | = 30 V / μm.

  When the undercoat layer 110 cannot withstand this electric field strength: EA, charge leakage occurs from “the place with the weakest insulation resistance” of the undercoat layer 110 due to hole blocking, and the holes reach the surface of the photoreceptor. The charge distribution on the surface is generated by canceling the negative charge on the surface. By scanning this state with an electron beam and detecting secondary electrons, it is possible to identify the “charge leak location (FIG. 3C)” due to dielectric breakdown on the order of μm.

In the case of evaluating the insulation resistance using the latent image carrier as a dielectric sample, the total amount of charge applied to the sample is desirably “1E-8 coulomb / mm ² or more” per unit area.
Total charge per unit area (charge density): Cm is expressed as follows by irradiation current: A, irradiation area: S, irradiation time: t Cm = A · t / S
For example, irradiation current: 5E-10A, irradiation area: 1 mm ^2, irradiation time: may be 20 seconds. The irradiation time: t should be increased in proportion to the irradiation area: S. If the irradiation current A is increased, a shorter time is required. When the total charge amount irradiated to the sample is increased by extending the irradiation time or the like, the charge leak portion becomes more noticeable.

For example, if the irradiation current is 1E-9A and the irradiation area is 1 mm ² for 5 minutes, the total charge amount is 3E-7 coulomb / mm ² . The difference is clear.

  If the withstand voltage required for the latent image carrier is usually 30 V / μm or higher, about 40 V / μm is required. Under this condition, it is preferable that “the charge leak region (the total area of the evaluation region described above: the area of the charge leak region with respect to SA: the percentage of s) is 1% or less”. If the charge leak region is 1% or less, it is known from experience that “the output image is not noticeable as background stain”.

Accordingly, the “condition for good latent image carrier” is that when a sample is irradiated with electrons of 1 nanocoulomb / mm ² or more under a condition that the withstand voltage is 30 V / μm or more and 40 V / μm or less, That is, the percentage of the area of the insulating region (the region of the evaluation region that is not broken down ) with respect to the evaluation region area is 99% or more.

FIG. 4 shows a measurement result when the latent image carrier is continuously irradiated with an irradiation time: t = 4 minutes with an irradiation current A: 1E-9A and an irradiation area S: 1.47 mm ² . The charge density Cm irradiated during this period was Cm = At / S = 1.6E-7 coulomb / mm ² .
At this time, the smaller the “area ratio of the region where charge leakage occurs”, the higher the insulation resistance.

  FIG. 4A shows a “bad sample” in which the ratio of charge leakage area is 1.2%, that is, the insulation resistance region is 98.8%, and soiling easily occurs. In FIG. 4B, the charge leak area ratio is 0.4%, and the “hole size” is small.

In the case of a latent image carrier, “insulation resistance is high, and the smaller the number of charge leak regions where charges leak, the better,” if limited to charge leakage, but if the insulation resistance is too high, “when exposed, sufficient There is a risk that the potential does not decrease. Considering this point, it can be evaluated that a photoconductor having a charge leak region area of 0.05% to 1.0% of the evaluation region area is a good photoconductor.

FIG. 5 shows another embodiment of the insulation resistance measuring apparatus . In order to avoid complications, the same reference numerals as those in FIG. The parts denoted by the same reference numerals as those in FIG. 1 are the same as those in the form of FIG. 1, and the description of FIG.

  In the embodiment of FIG. 5, the dielectric sample 01 is a latent image carrier and is a “function-separated type photoconductor” described with reference to FIG. The dielectric sample 01 is formed in a drum shape, which is a general form of a photoconductive photoconductor, and is rotated at a constant speed in the direction of the arrow (counterclockwise) by a driving means (not shown). After the sample 01 is set in the casing 30A, the inside of the casing 30A is highly decompressed by the suction means 32.

  “Charging means” indicated by reference numeral 42 is, for example, a contact-type charging means such as a charging brush or a charging roller, and uniformly charges the dielectric sample 01 in a casing under reduced pressure. At this time, the sample 01 is rotated at a constant speed in the direction of the arrow (counterclockwise). Of course, as in the example described with reference to FIG. 1, the dielectric sample 01 can be charged by charging using an electron beam.

  Scanning of the electron beam by the electron beam irradiation unit 11A may be performed by two-dimensionally deflecting the electron beam as in the embodiment of FIG. 1, but the dielectric sample 01 rotates at a constant speed in the direction of the arrow. Since scanning is performed, the electron beam can be deflected one-dimensionally in a direction orthogonal to the drawing, and the two-dimensional scanning can be realized by combining this deflection and the rotation of the dielectric sample 01.

  Prior to measuring the insulation resistance, the static elimination lamp indicated by reference numeral 29A uniformly irradiates the surface of the dielectric sample 01 rotating at a constant speed, and the state of the dielectric sample 01 is referred to as “appropriate state suitable for measurement”. To do.

In each embodiment described above, a case has been described using an electron beam as a charged particle beam, of course, other charged particle beam, for example, are also considered to use "ion beam", in which case the A liquid metal ion gun or the like may be used instead of the electron gun.

FIG. 6 is a simplified flow chart illustrating the measurement procedure in the embodiment described above.
A dielectric sample (referred to as a latent image carrier) is set in a measuring device (held by a holding means) and charged by electron beam irradiation. Next, electron beam scanning is performed to detect secondary electrons generated in the dielectric sample, and a two-dimensional image is mapped based on the detection result. Next, the “data at each pixel of the mapped two-dimensional image” is binarized at a predetermined threshold level. In this state, a monochrome image as shown in FIGS. 4A and 4B is obtained.

  Subsequently, the charge leak location is specified, the total area of the charge leak location (black portion) (obtained as the sum of the number of black pixels) is obtained, the area percentage with respect to the evaluation region is obtained, and the latent image is determined according to the result. It is evaluated whether or not the carrier is a non-defective product.

It is a figure for demonstrating one Embodiment of an insulation resistance measuring apparatus. It is a figure for demonstrating the detection of a secondary electron. FIG. 5 is a diagram for explaining charge leakage due to dielectric breakdown in a function-separated type photoreceptor. It is a figure which shows the example of a measurement result. It is a figure for demonstrating one form of an insulation resistance measuring apparatus . It is a flowchart which shows the procedure of insulation resistance measurement.

Explanation of symbols

0 Dielectric sample 11A Electron beam irradiation part
23 Plate-shaped holding part 25 Charged particle trap

Claims (7)

Insulation resistance for evaluating the insulation resistance of the sample based on a detection signal obtained by two-dimensionally scanning the surface of the sample that has been charged and applied an electric field strength in the thickness direction with an electron beam. A measuring method,
The sample is a latent image carrier,
The desired region of the sample surface is charged by two-dimensionally scanning an electron beam for charging to give a predetermined electric field strength in the thickness direction of the sample in the desired region,
The charged potential of the sample corresponding to the electric field intensity is two-dimensionally scanned with an electron beam for potential detection, and the charged state of the desired region is two-dimensionally imaged by detecting secondary electrons accompanying this scanning. acquired as data by the image data the method cormorants line evaluation of the insulation resistance of the sample,
When the secondary electron emission ratio δ is defined by the ratio Not / Nin of the number of secondary electrons released to the number of incident electrons Nin irradiated in the two-dimensional scanning by the electron beam,
The acceleration voltage of the electron beam that performs two-dimensional scanning with the charging electron beam is higher than the acceleration voltage E2 that becomes 1 after the secondary electron emission ratio δ from the sample surface at the time of scanning exceeds the maximum. Set acceleration voltage E (> E2)
The insulation resistance measuring method, wherein the two-dimensional scanning with the electron beam for detecting the potential is performed with an irradiation current amount different from that in the scanning with the electron beam for charging. In the insulation resistance measuring method according to claim 1,
A method for measuring insulation resistance, wherein an electric field strength of 10 V / μm or more is given in the thickness direction of a sample by two-dimensional scanning with an electron beam for charging. In the insulation resistance measuring method according to claim 1 or 2,
A method for measuring insulation resistance, comprising: detecting a charge leak point in a sample based on two-dimensional image data acquired from a detection signal obtained by detecting secondary electrons. A method of evaluating suitability as a latent image carrier using a latent image carrier as a sample,
Among the evaluation area areas for evaluating the insulation resistance in the sample, when the area that does not break down is regarded as the insulation resistance area,
When the electric field strength applied in the thickness direction is 30 V / μm or more and 40 V / μm or less, the sample is irradiated with an electron beam for charging 1E-8 coulomb / mm ² or more,
Area of the measured resistance to dielectric edge regions by resistance insulating measuring method according to any one of claims 1 to 3, determine the suitability of the latent image bearing member by whether at least 99% of the evaluation region area A latent image carrier evaluation method characterized by the above. In the latent image carrier evaluation method according to claim 4,
When the electric field intensity in the thickness direction of the sample is 30 V / μm or more and 40 V / μm or less, when the electron beam for charging is irradiated with 1E-8 coulomb / mm ² or more , the area of the charge leak region is the evaluation region. A method for evaluating a latent image carrier, wherein the latent image carrier is evaluated as having a good latent image carrier when the area is 0.05% or more and 1.0% or less. Holding means for holding a latent image carrier which is a sample to be evaluated for insulation resistance;
Charging means for charging the sample held by the holding means and applying electric field strength in the thickness direction of the sample;
Scanning means for scanning the surface of the charged sample with a charged particle beam;
Signal detection means for obtaining a detection signal by scanning by the scanning means;
Evaluation means for evaluating the insulation resistance of the sample based on the signal detected by the signal detection means,
The charging means two-dimensionally scans a desired two-dimensional region of the sample with a charging electron beam,
The scanning unit is configured to two-dimensionally scan the desired two-dimensional region with an electron beam for detection in which the irradiation current in the charging unit is switched.
When the secondary electron emission ratio δ is defined by the ratio Not / Nin of the number of secondary electrons released to the number of incident electrons Nin irradiated in the two-dimensional scanning by the electron beam,
In the two-dimensional scanning by the charging electron beam, the acceleration voltage E2 at which the acceleration voltage of the electron beam of the scanning means becomes 1 after the secondary electron emission ratio δ from the sample surface accompanying the scanning exceeds the maximum. Insulation resistance measuring apparatus, characterized in that it is set at a higher acceleration voltage E (> E2). In the insulation resistance measuring apparatus according to claim 6,
The charging means has a condenser lens and an aperture for the electron beam;
An insulation resistance measuring apparatus, wherein the amount of irradiation current is switched between when the sample is charged and when a detection signal is obtained by the condenser lens and / or aperture.

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